1. Field of the Invention
The present invention relates to a level shifter for converting a level of an input signal to another level.
2. Description of the Related Art
Same flash electrically erasable programmable read only memories (EEPROM) and other semiconductor nonvolatile memories perform a write operation or a read operation by using a control signal set to a plus high voltage PV and a minus high voltage MV in addition to a power supply voltage Vcc level and a ground voltage GND level.
For this, such flash EEPROMs etc. are provided with a level shifter for converting the power supply voltage Vcc level or the ground GND level to the plus high voltage PV level or the minus high voltage MV level and outputting the converted signal.
In general, a level shifter is constituted by a separate circuit for converting the control signal to the plus high voltage and circuit for converting the control signal to the minus high voltage or by a latch circuit with inputs and outputs connected cross-wise and a transmission gate and transmitting the input signal to an input-output terminal through the transmission gate ad then boosting the power supply voltage of the latch circuit.
However, the former circuit becomes large in size, while with the latter circuit, it is necessary to configure the transmission gate by only an n-channel metal insulator semiconductor (MIS) transistor at the plus high voltage side and only a p-channel MIS transistor at the minus high voltage side in order to prevent the boosted voltage from flowing backward to an input terminal of the input signal. Due to this, in the case of a low power supply voltage, the voltage of the input signal will be affected by the threshold voltage of the transmission gate and, as a result, the signal will not be able to be transmitted. As a result, it becomes necessary to form a transistor with an especially low threshold voltage, which increases the cost of the production.